There are a variety of stem assemblies for securing the handlebars of a bicycle to the front fork of a bicycle frame. Such assemblies generally consist of a tubular barrel portion which connects to the front wheel fork of a bicycle frame and a head portion which is adapted to receive and clamp the bicycle handlebars. These stem assemblies generally are either made as a single piece unitary item or as a two-piece item. If made in two pieces, one piece is a tubular barrel and the other piece is a clamping head which is welded or brazed to the barrel. Examples of such two-piece stems are disclosed in U.S. Pat. No. 4,322,087 and German Pat. No. 2,717,316.
One piece stems are generally made either from machined forging or from die stamped and formed sheet metal. One example of a one-piece sheet metal stem is disclosed in U.S. Pat. No. 2,505,648.
One-piece sheet metal stem assemblies have heretofore been very popular because of their effectiveness in safely securing handlebars to the frame of bicycles and the economics of their manufacture. The economics of the one-piece sheet metal stem derive from the fact that the one piece stem is made from relatively inexpensive sheet metal with a minimum of hand labor. But such one-piece stems require a very large capital expenditure for the dies and tooling utilized in manufacturing such relatively complex shaped parts. Furthermore, it is relatively expensive to maintain complex tooling in a condition in which it consistently produces high quality parts without weak points in the stem subject to failure. The throat area of the one-piece stem between the barrel and head is particularly subject to failure if improperly shaped and configured. If imperfectly formed as, for example, by worn or improperly maintained tooling, the resulting stem is subject to failure in use and particularly to fatigue failure.
An alternative to forming the stem as a unitary structure upon relatively expensive tooling has been to form the stems as two pieces and then weld or braze those pieces together. But to date, no two-piece stem structure has been available which has both the rugged strength required for safe bicycle usage and the favorable economics of manufacture which would enable it to compete effectively with one-piece sheet metal stems.
Therefore, it has been one objective of this invention to provide a bicycle stem assembly which is as rugged and resistant to failure in use as prior art one-piece stems, but which may be manufactured without the need for the expensive tooling heretofore required for the manufacture of one-piece sheet metal stems.
It has been another object of this invention to provide a strong, rugged two-piece stem assembly which may be made from sheet metal.
Still another objective of this invention has been to provide a bicycle stem assembly which may be manufactured less expensively and with less expenditures for tooling than current one-piece sheet metal stems, but which is equally as strong and resistant to failure in use.